Could anyone help me understand the green question.
Thank you.
Hello,
I've attached a sketch of the situation (see attachment)
The viewable angle of the earth looking from a satelite $\displaystyle S_a$ is twice as large as the angle $\displaystyle \alpha$.
The satelite, the center of the earth and the radius of the earth form a right triangle.
$\displaystyle \sin(\alpha)=\frac{R}{R+d}$
If you know d then you can calculate the viewable angle $\displaystyle = 2\cdot \alpha$ with R = 6365 km.